In the case of rotating electrical machines having slip-rings, for example a polyphase asynchronous motor in the form of a slip-ring rotor, currents are transmitted by means of appropriate brushes via the slip-rings which rotate with the shaft. One example of a rotating electrical machine such as this is illustrated, partially, in FIG. 1. The rotating electrical machine 10 illustrated there, with its machine axis 17, comprises a rotor, which can rotate about the machine axis 17, with a central body 11 which merges at the end into a shaft 16. A rotor laminated body 12 is seated on the central body 11 and a rotor winding 13 is accommodated in it, which rotor winding 13 has a rotor end winding 13′ at the end. The rotor 11, 12, 13 is concentrically surrounded by a stator laminated body 15, in which a stator winding with a corresponding stator end winding 15′ is accommodated. A plurality of (four) slip-rings 14 are arranged on the outside of the shaft 16 and are used to transmit current between the rotor and the outside world. In the case of the machine illustrated in FIG. 1, the power loss must be dissipated by means of specific cooling devices.
When machines of this type are highly loaded, particular attention must be paid to cooling in the area of the slip-rings. Because of the high electric and mechanical (friction) load on the brushes and the slip-rings 14, an increased temperature development occurs in this area. Since the brushes react by increased wear to any discrepancy from the optimum operating temperature, and can be completely destroyed above a critical temperature, appropriate cooling must be provided for these components.
As is shown in FIG. 2, the conventional design of the slip-ring area envisages a continuous shaft 16 on which the slip-rings 14 are mounted. With this design, the slip-rings 14 can be cooled only to a highly restricted extent. The cooling air (or some other cooling medium) would have to flow onto the slip-rings 14 from the outside. However, this is difficult because the slip-rings 14 rotate. Cooling from the interior, with the air flowing radially outwards from the interior of the shaft 16, is impossible because of the closed shaft 16. On the other hand, it is problematic for mechanical strength reasons to provide the shaft 16 with an appropriately large number of openings.
EP-A1-0 052 385 describes a slip-ring arrangement for electrical machines, in which the slip-rings are provided with axial cooling gas holes, which are cut in the form of grooves or slots in the slip-ring surface. Cooling gas passes radially outwards via the grooves or slots into the cooling gas holes, with heat being absorbed, and is dissipated via these holes by means of a suction fan. However, the design of a cooling configuration such as this is very complex.
In order to improve the cooling in the area of the slip-ring arrangement, DE-A1-32 32 102 describes that each slip-ring be subdivided into a number of individual slip-rings, which are shrunk onto intermediate shrink rings which are isolated from the slip-ring shaft. Cooling air fans are arranged in front and behind the slip-rings on the intermediate shrink rings. This solution also involves a complicated design, and very demanding cooling air routing.